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... Several Canadian jurisdictions are moving toward ending the twice-yearly clock change, but a new analysis published in CMAJ (Canadian Medical Association Journal) www.cmaj.ca argues that eliminating the clock change is only half the decision: governments must also decide whether to adopt permanent standard time or permanent daylight saving time.
Both choices have trade-offs. Permanent daylight saving time keeps evenings lighter, which may support recreation, social activity, commuting, and some economic activity.
But it also pushes sunrise an hour later, leaving more people waking, travelling to school, and commuting to work, in darkness during the winter. Permanent standard time preserves more morning light and better aligns clock time with human circadian biology, although evenings become darker earlier.
"Ending the clock change solves one problem, but it creates another decision: which time should we live on year-round?" says lead author Dr. Raymond Lam, professor of psychiatry at the University of British Columbia (UBC), Vancouver, BC. "The health evidence points to standard time, largely because morning light matters for our body clocks, sleep, and mood."
Weighing the trade-offs
Major sleep and chronobiology organizations recommend permanent standard time. The authors note that morning light helps synchronize the body's circadian clock, while evening light delays it. Permanent daylight saving time, therefore, works against circadian alignment during winter by reducing morning light while extending evening light. ...
Our biological clocks need morning light to stay synchronized with the 24-hour day. Permanent daylight saving time moves that light an hour later just when winter mornings are already darkest."
Dr. Ralph Mistlberger, professor of psychology, Simon Fraser University, Vancouver, BC
The effects may be especially important for mood and sleep. An estimated 1% to 3% of people in Canada experience seasonal affective disorder (SAD), while as many as 15% experience milder seasonal changes in mood, sleep, appetite, and energy. The authors also point to geographic studies showing that people living farther west within a time zone - where sunrise occurs later by the clock - experience several adverse health outcomes. ...
